TM 5-3805-298-23-2
0174
WIRING HARNESS OPEN CIRCUIT TEST
000174
An open circuit is a failure of any electrical circuit that results in no flow of electrical current. An open circuit is
usually caused by failed electrical wires or a poor connection of wiring harness connectors. If an electrical wire or a
connection is broken, flow of electrical current through the circuit is interrupted. A normal circuit will have 5.0 ohms
or less of resistance.
Test Procedure
000174
1. Use electrical schematic of machine to identify connectors and wire numbers of suspected circuits.
2. Turn ignition switch and battery disconnect switch to OFF position (TM 5-3805-298-10).
3. Isolate wiring harness by disconnecting each end of suspect circuit from component, and in-line harness
connector, or an ECM connector from ECM.
4. At suspect connector end of disconnected wiring harness, place a jumper wire between terminal of suspect
wire and machine ground.
5. Select resistance/ohms setting on digital multimeter.
6. At other end of wiring harness, use digital multimeter probes to measure resistance between terminal of
suspect wire and machine ground.
a. If resistance is 5 ohms or less, wiring harness circuit is OK.
b. If resistance is greater than 5 ohms, there is an open in suspect wire. Replace affected wiring harness.
END OF TASK
WIRING HARNESS SHORT CIRCUIT TEST
000174
A short circuit is a failure of an electrical circuit that results in undesired electrical current. Usually, a short circuit is
a bypass of circuit across a load. For example, a short across wires in a circuit for a lamp produces too much
current in the wires but no current is delivered to the lamp. The lamp is shorted out. There should be no continuity
between a particular circuit and other unrelated circuits.
Test Procedure
000174
1. Use electrical schematic of machine to identify connectors and wires of suspected circuits.
2. Turn ignition switch and battery disconnect switch to OFF position.
3. Isolate wiring harness by disconnecting each end of suspect circuit from component, and in-line harness
connector, or an ECM connector from ECM.
4. Select diode/continuity on digital multimeter.
5. Place one digital multimeter lead on terminal of suspect wire.
6. Use other digital multimeter lead to test for continuity between suspect wire in wiring harness connector and all
other terminals in wiring harness connector and also to frame ground. There should be no continuity.
a. If digital multimeter indicates infinity, "OL", or greater than 1M ohms, wire is OK, not shorted. Proceed to
next test as directed.
b. If digital multimeter indicates 1M ohms or less, wire is shorted. Verify test results, if results are repeated,
replace affected wiring harness.
END OF TASK
0174-12
